use updated brew cask command

[esthor]

What's this PR do?

• Updates brew install command to work with latest homebrew

Any background context you want to provide? (if appropriate)

brew cask install blurred
Error: `brew cask` is no longer a `brew` command. Use `brew <command> --cask` instead.

So we need to use: brew install --cask blurred instead. and it works:

brew install --cask blurred
==> Caveats
blurred is built for Intel macOS and so requires Rosetta 2 to be installed.
You can install Rosetta 2 with:
  softwareupdate --install-rosetta --agree-to-license
Note that it is very difficult to remove Rosetta 2 once it is installed.

==> Downloading https://github.com/dwarvesf/blurred/releases/download/v1.2.0/Blurred.1.2.0.dmg
==> Downloading from https://objects.githubusercontent.com/github-production-release-asset-2e65be/241799295/b6f5f080-b54a-11ea-9f5b-138509239
###################################################################################################################################### 100.0%
==> Installing Cask blurred
==> Moving App 'Blurred.app' to '/Applications/Blurred.app'
🍺  blurred was successfully installed!